Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Lumi scans with wakefields in Merlin Lumi scans with wakefields in Merlin Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop at SLAC December 13 th, 2007

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Offset and angle scan from TESLA TDR Luminosity drops fast with small change of offset and/or angle How is the luminosity change for the ILC? Now check with beams generated by MERLIN: effect of wakefields (w/o and with quadrupole errors) influence of HOM and RF couplers (with wakefields) Results from beam-beam simulation with GUINEA-PIG from TESLA TDR TESLA parameters:  y = 5nm,  y = 12  rad

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, MERLIN beam parameters Merlin beam: 10 4 or 10 5 particles -> 5k or 50k per beam: generated with ILC2006c lattice file:  x  600 nm  x = 4.1 nm (nom IR: 5.7nm)  x = 8 mmmrad (nom IR : 10 mmmrad)  y = 0.02 mmmrad (nom IR : 0.04 mmmrad) no undulators, with BDS zz y y’ higher lumi than in RDR (~ cm -2 s -1 )

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Offset & angle scans: no quadrupole error Ideal machine, only influence of longitudinal wakefields 2 x 50 beams (different random numbers) Essentially no difference visible between the two samples  longitudinal wakefield has no negative influence on lumi offset scan angle scan

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Quadrupole error Examples for 2 different quad error configurations mm Ideal machine: only longitudinal wakefields visible First test: to see the effect of vertical wakefields we need to be off-axis in vertical direction  introduce quadrupole errors with  = 500  m Run in 50 different configurations of quadrupole errors and with steering

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Offset & angle scans: with quadrupole errors 2 x 50 beams (different random numbers) and quadrupole errors(  y = 500  m)  Wakefield sample looks better than non-wakefield sample  Stronger effect on beam angle than on offset offset scan angle scan

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Difference wakefield/ no-wakefield sample Wakefields cause the energy spread to be smaller - no wakefield - wakefield no wakefield with wakefield z z energy spread (because the RF angle (5.3˚) is tuned to be optimal with wakefields)

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Comparison of wakefield samples w/ and w/o quad errors To extract the effect of quad errors with wakefields on lumi compare wakefield samples with and without quad errors: L no QE = (2.9 ±0.1) cm -2 s -1 L QE = (2.7 ±0.2) cm -2 s -1  Loss due to vertical wakefields with only quad errors:  9%  Angle and offset scans don’t help  need more studies with realistic errors introduced in cavities, BPMs,… offset scan angle scan

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Reminder: HOM and RF couplers Merlin implementation: see talk of Dirk Krücker

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Offset & angle scan: comparison of old/new HOM coupler position old new angle scan offset scan (for  y =0)  Old coupler position needs stronger tuning in angle  After angle tuning loose  12% in lumi with old coupler pos.

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Kick from RF field + coupler wakefields RF kick: quite strong, but steering works here: L no RF = (2.9 ± 0.1) cm -2 s -1 L RF, tuned = (3.0 ± 0.1) cm -2 s -1 consistent within error  effects of RF and coupler kicks can be tuned away blue curve is with linear tuning in waist, dispersion, coupling (see talk of Dirk Krücker) offset scan angle scan

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Waist scan with MERLIN beam Waist scan for beam with RF and coupler kicks for best angle (  y /  y = -0.4) Waist tuning: gain 3% of lumi

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Conclusions and Outlook Longitudinal wakefields have no negative influence on lumi No lumi gain due to offset/angle scans with vertical quad misalignment and wakefields New coupler geometry better than old one (gain ~12% of lumi) Influence of RF kick can be tuned away (at least if the rest of the accelerator is ideal…), linear tuning helps here Waist scan: gain ~3% of lumi with optimal waist To Do: Use more realistic accelerator errors and alignment to check influence of vertical wakefields and RF kicks (errors on cavities, BPMs,…)

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Backup slides

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Tuning the beam In reality: tune the beam to have the mean of the beam centered around 0 in the interaction point.  Do it also in MERLIN (but no change in shape)  see talk of Dirk Krücker for details

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Offset scan (ILC2006c): quadrupole error and tuned Looks similar to untuned sample, slightly better for the no wakefield case 2 x 50 beams with different quadrupole errors (  y = 500  m) tuned to have the mean centered around 0

Isabell-A. Melzer-Pellmann LET Beam Dynamics Workshop, Angle scan (ILC2006c): quadrupole error and tuned Looks similar to untuned sample. Looks similar to untuned sample, slightly better for the no wakefield case 2 x 50 beams with different quadrupole errors (  y = 500  m) tuned to have the mean centered around 0